This invention relates to a tool holder for a hand held electrically powered hammer and to a hand held electrically powered hammer incorporating such a tool holder. In particular this invention relates to tool holders for demolition hammers.
Such hammers generally comprise a housing within which is located an electric motor and a gear arrangement for converting the rotary drive of the motor to a reciprocating drive to drive a piston within a hollow spindle or cylinder, which spindle is located within the hammer housing. A ram is located in front of the piston within the spindle so as, in normal operating conditions, to form a closed air cushion within the spindle between the piston and the ram. The reciprocation of the piston reciprocatingly drives the ram via the air cushion. A hollow piston arrangement may be used, as is well known in the art. A beatpiece is generally located within the spindle and transmits repeated impacts that it receives from the ram to a tool or bit releaseably mounted for limited reciprocation in front of the beatpiece in a tool holder portion. The impacts on the tool or bit are transmitted to a workpiece against which the tool or bit is pressed in order to break up or make a bore in the workpiece.
Some hammers may also be employed in combination impact and drilling mode in which the tool holder, and hence the tool inserted therein, will be caused to rotate at the same time as the tool is struck by the beatpiece. The present invention is also applicable to such hammers.
A common form of chiselling tool or bit, for performing heavy duty work is a hex-shanked tool or bit. The portion of the tool which is locked within the tool holder of the hammer has a hexagonal transverse cross-section. The bore in the tool holder which receives the hexagonal shank portion generally has a corresponding hexagonal transverse cross-section and so the tool is non-rotatably fitted within the tool holder. The hexagonal portion is formed on one of its flats with an axially extending groove which is closed at both its ends. The hex-shanked tool can be locked within the tool holder to enable limited reciprocation of the tool within the tool holder. Traditionally, a cross bolt arrangement is used to lock the tool within the tool holder. The bolt extends tangentially of the toolholder to engage the groove in the tool. The bolt can be retracted or pivoted outwardly to allow insertion or removal of the tool.
An alternative to a hex-shanked tool or bit for use on hammers is an SDS-type tool or bit. The SDS-type tools have a tool shank which is provided with irregularly positioned axially extending grooves, open at their rearward ends which grooves co-operate with radially inwardly extending splines in the bore of the tool holder. Thus, the tool is non-rotatably fitted within the tool holder. In addition the SDS-type tools have two axially extending grooves which are closed at their ends and which are each engageable by a locking body in order to lock the tool within the tool holder so as to allow limited reciprocation of the tool within the tool holder. Tool holders for SDS-type tools generally have one or two radially shiftable locking bodies which can be releaseably locked within one of the, or each, groove of a tool inserted into the tool holder.
It is an aim with tool holders for hammers to have a simple, compact and ergonomic design in which the locking body can move between its radially inward locked position and its radially outward unlocked position smoothly. It is also advantageous to provide automatic locking of a tool within the tool holder, to enable the tool to be locked in the tool holder automatically by simply pushing the tool into the tool holder, without manually actuating the tool holder.
The present invention aims to overcome at least some of the problems discussed above by providing a simple, compact and ergonomic design of tool holder.
According to a first aspect of the present invention there is provided a tool holder for an electrically powered hammer comprising:
a tube-like tool holder body which can be fitted to or formed at the front of a hammer and having a forward end for non-rotatably receiving a shank of a tool or bit wherein said forward end is formed with a single axially extending slot;
a single locking body extending through said slot for releasably engaging an axially extending closed groove formed in a tool fitted in said forward end of the tool holder body; and
a locking member which extends around the tool holder body and in a locked position locks the locking body in a radially inward position in which the locking body is engageable with the groove in the tool and in a release position allows the locking body to move into a radially outward position to allow a tool to be inserted into or removed from the forward end of the tool holder body;
wherein the locking member is shiftable in a direction transverse to the fore-aft axis of the tool holder body to allow the locking body to move into a radially outward position.
By making the locking member shiftable in a direction transverse to the fore-aft axis of the tool holder the member can simply be shifted transversely between a locked position in which it engages the locking body to hold the locking body within the groove of a tool or bit inserted into the tool holder body and an unlocked position in which the locking body is free to move radially outwardly to enable insertion and/or removal of the tool or bit.
The locking member may extend all the way around the tool holder body and may, for example, be a locking ring.
To shift the locking member, it is preferred that there is provided a manually actuable tool release member for moving the locking member which tool release member can be actuated to move the tool release member between a locked position which corresponds to the locked position of the locking member and a release position which corresponds to the release position of the locking member. Preferably, the manually actuable tool release member can be actuated to move the locking member between the locked position and an intermediate position, in which intermediate position the locking member is shiftable in a direction transverse to the fore-aft axis of the tool holder body to its release position to allow the locking body to move into a radially outward position. Thus, with the locking member in its intermediate position, the locking body can shift the locking member to its release position when the locking body in urged radially outwardly by the shank of a tool or bit. For a particularly, ergonomic and simple design, the manually actuable tool release member may be axially shiftable on the tool holder body.
In one embodiment of the present invention, in the locked position the locking member can engage a protrusion on the tool holder body in order to lock the locking member in its locked position. Then the tool release member is preferably moveable to axially shift the locking member between the locked position of the locking member in which it engages the protrusion on the tool release sleeve and the intermediate position of the locking member in which the locking member does not engage the protrusion and so is free to shift transversely into its release position.
The tool release member may be a tool release sleeve which is co-axial with the tool holder body and within which is mounted the locking member so as to enable locking member, when in the intermediate position to shift with respect to the tool release sleeve in a direction transverse to the fore-aft axis of the tool holder body. For a robust and simple design the locking member may be mounted within the tool release sleeve, between a first set of radially inwardly directed teeth of the sleeve and a second set of radially inwardly directed teeth of the sleeve.
To enable automatic movement of the locking member into its locked position, the locking member may be biased by at least one spring member into the locked position. Alternatively, or in addition a biasing member, preferably a biasing ring may extend around, preferably all the way around the tool holder body and be used to bias the locking member into the locked position.
In a preferred embodiment of the present invention which enables insertion of a tool or bit within the tool holder body without manual actuation of the tool release member, the slot in the tool holder body extends rearwardly of the locking body, the biasing ring biases the locking body forwardly within the slot into its locked position and the locking body and the locking member are axially moveable together such that insertion of a tool within the tool holder body pushes the locking body axially rearwardly within the slot and thereby pushes the locking member and biasing ring axially rearwardly against the biasing force of the biasing ring and into an intermediate position, in which intermediate position the locking member is shiftable in a direction transverse to the fore-aft axis of the tool holder body to allow the locking body to move into a radially outward position. Then the tool can be inserted further into the tool holder body and the biasing ring biases the locking member and thereby the locking body into its locked position in which the locking body engages the groove in the tool or bit to lock the tool or bit within the tool holder body.
It can be arranged for the biasing ring to engage the tool release member so that axial movement of the biasing ring causes axial movement of the tool release member. This is of particular advantage when the tool is a hex-shanked tool which can be inserted into the tool holder body in an incorrect orientation in which the groove in the tool does not face the locking body. When a tool is incorrectly inserted in the wrong orientation, then the biasing ring cannot move forwardly to urge the locking member and thereby the locking body into its locked position because the shank of the tool traps the locking body in its radially outward position. This problem is made immediately apparent to the user of the hammer due to the failure of the tool release member to move into its locked position, because the tool release member cannot move into its locked position due to its engagement with the biasing ring. The biasing ring may engage a set of teeth of the tool release sleeve described above, which teeth limit the movement of the biasing ring within the sleeve.
In a particularly simple and compact design, the locking member is shiftable in a locking assembly comprising a forward support member located forwardly of the locking member and a rearward support member located rearwardly of the locking member. This locking assembly is preferably axially fixed with respect to the tool release member, particularly where the tool release member is an axially shiftable tool release sleeve. The rearward support member may have the dual function of also being the biasing ring.
In order to damp the transfer of the impact on the locking body to the tool holder body, on entry of a hammer incorporating the tool holder-into idle mode, the forward movement of the locking body within the slot may be limited by a damping arrangement which arrangement is axially fixed against forward movement on the forward portion of the tool holder body. Preferably, the damping arrangement comprises a metal ring, a resilient ring, which is deformable to damp the impact, located forwardly of the metal ring and a fixing ring located forwardly of the resilient ring.
The tool holder according to the present invention is particularly suited to a hex-shanked tool having a shank with a transverse hexagonal cross-section. However, it can also be used in relation to SDS-type tools and other tool types which are used in relation to hammers.
According to a second aspect of the present invention there is provided an electrically powered hammer preferably having a pneumatic striking mechanism comprising a piston and ram located so as to reciprocate within a hollow spindle and additionally including a tool holder as described above.